Electroacoustic transducer

ABSTRACT

An electroacoustic transducer includes a magnetic circuit unit that forms a magnetic gap, a voice coil inserted into the magnetic gap, and a diaphragm to which the voice coil is connected. The diaphragm has a central portion having an outer peripheral edge and an annular portion disposed underneath the central portion. The annular portion has an outer peripheral edge corresponding to the outer peripheral edge of the central portion, and an inner peripheral edge secured to the magnetic circuit unit. The diaphragm further has a joint portion formed at the outer peripheral edges of the central and annular portions, and the outer peripheral edges are joined together. The voice coil is disposed underneath the central portion of the diaphragm and joined to the joint portion.

REFERENCE TO THE RELATED APPLICATIONS

This application claims priority under 35 U.S.C. § 119 to JapanesePatent Application No. JP2007-171499 filed on Jun. 29, 2007, the entirecontent of which is hereby incorporated by reference.

BACKGROUND OF THE INVENTION

1. Technical Field of the Invention

The present invention relates to an electroacoustic transducer that maybe incorporated into electronic devices such as mobile phones andpersonal digital assistants (PDAs) to inform the user of an incomingcall by vibrating a diaphragm.

2. Description of the Related Arts

Conventionally, mobile communications devices such as mobile phones andPDAs are arranged to inform the user of an incoming call by selectivelygenerating beep sound or melody sound, or vibrating the housing of thedevice instead of producing sound. Such an electroacoustic transducer isdisclosed, for example, in Japanese Patent Application Publication No.2003-143676. The electroacoustic transducer has, as shown in FIG. 10, amagnetic circuit unit including a cup-shaped yoke 22 and a combinationof a circular columnar permanent magnet 24 and a top plate 25 that aresuccessively stacked on the inner bottom surface of the yoke 22. Amagnetic gap is formed between the inner peripheral surface of the yoke22 and the outer peripheral surface of the top plate 25. A voice coil 27disposed under the diaphragm 26 is inserted into the magnetic gap. Thediaphragm 26 is a thin resin member having a central dome portion 26 aand an annular portion 26 b radially extended from an edge of thecentral dome portion 26 a. The voice coil 27 is bonded to a flatboundary portion between the central dome portion 26 a and the annularportion 26 b. The peripheral edge of the annular portion 26 b is laid onthe upper end surface of a casing 23, and a retaining ring 28 is placedon the peripheral edge of the annular portion 26 b. The casing 23 iscovered at its upper side with a shallow dish-shaped protector 29 thatis a thin metallic member bored with a plurality of sound release holes29 a. The protector 29 is bonded to the outer peripheral surface of thecasing 23. The casing 23 is provided with a plurality of air vents 30.When supplied with a sound signal current, the voice coil 27 vibrates,and thus the diaphragm 26 vibrates to generate a sound or a voice.

Main factors that determine the characteristics of the electroacoustictransducer are as follows: Magnetic force B; diameter of a voice coil L;electric current I; mass of a vibration system Mo (mass of the vibrationsystem including the voice coil, the diaphragm, the adhesive, etc.);stiffness So (indicating the degree of difficulty in movement of thediaphragm, which is determined mainly by the annular portion thereof);and diaphragm effective area Sd (area of the diaphragm used for soundgeneration). The sound pressure may be given by:

(Sound pressure)=A×B×L×I×Sd/(So×Mo)

where A is a variable characteristic of each individual speaker.

SUMMARY OF THE INVENTION

With the structure of the electroacoustic transducer disclosed inJapanese Patent Application Publication No. 2003-143676, it is difficultto increase the sound pressure by enlarging the central dome portion ofthe diaphragm, which constitutes the main part of the diaphragmeffective area.

It is an object of the present invention to provide an electroacoustictransducer that enables the central dome portion of the diaphragm to beeffectively enlarged.

The present invention provides an electroacoustic transducer including amagnetic circuit unit that forms a magnetic gap, a voice coil insertedinto the magnetic gap, and a diaphragm to which the voice coil isconnected. The diaphragm has a central portion having an outerperipheral edge and an annular portion disposed underneath the centralportion. The annular portion has an outer peripheral edge correspondingto the outer peripheral edge of the central portion, and an innerperipheral edge secured to the magnetic circuit unit. The diaphragmfurther has a joint portion formed at the outer peripheral edges of thecentral and annular portions, and the outer peripheral edges are joinedtogether. The voice coil is disposed under the central portion of thediaphragm and joined to the joint portion.

In this electroacoustic transducer, the annular portion of the diaphragmis disposed underneath the central portion thereof. Therefore, thediaphragm effective area can be increased, and it becomes possible toobtain a high sound pressure.

Specifically, the central portion of the diaphragm may have an upwardlyconvex dome shape.

More specifically, the annular portion of the diaphragm may have anupwardly convex arcuate sectional configuration.

The electroacoustic transducer may be arranged as follows. The jointportion of the diaphragm has a tubular coil support extending coaxiallywith the voice coil, and the voice coil is mounted on the inner or outerperipheral surface of the coil support. With this arrangement, theinstallation of the voice coil is facilitated.

Specifically, the electroacoustic transducer may be arranged as follows.The coil support has an L-shaped sectional configuration having anannular support portion extending radially outward from the lower endedge of the coil support, and the voice coil is in contact with both theouter peripheral surface and the annular support portion of the coilsupport. With this arrangement, the installation of the voice coil isfacilitated, and the voice coil can be reliably retained.

As another specific example, the voice coil may be formed by being woundon the outer peripheral surface of the coil support. With thisarrangement, the formation and installation of the voice coil arefurther facilitated.

As still another specific example, the joint portion of the diaphragmmay have an annular extension extending radially outward from the jointportion of the diaphragm. With this arrangement, the effective area ofthe diaphragm can be increased.

The annular portion of the diaphragm may be either impermeable orpermeable to air. In a case where the annular portion of the diaphragmis permeable to air, the magnetic gap is filled with a liquid. This isdone to block communication between the spaces outside and inside thediaphragm.

More specifically, the electroacoustic transducer may be arranged asfollows. The magnetic circuit unit includes a yoke having a bottom wallportion and an annular peripheral wall portion extending upward from theperipheral edge of the bottom wall portion, and a combination of amagnet and a top plate that are successively stacked on the bottom wallportion of the yoke. The magnetic gap is formed between the peripheraledge surface of the top plate and the inner peripheral surface of theperipheral wall portion of the yoke. The bottom wall portion of the yokehas a through-hole formed at a position corresponding to the magneticgap to communicate between the outside of the magnetic circuit unit andthe inside of the yoke. This arrangement allows the voice coil tovibrate smoothly in the magnetic gap.

As another specific example, the electroacoustic transducer may bearranged as follows. The magnetic circuit unit includes a yoke having abottom wall portion and a pair of peripheral wall portions extendingupward from a pair of mutually opposing portions of the peripheral edgeof the bottom wall portion, and a combination of a magnet and a topplate that are successively stacked on the bottom wall portion of theyoke. The magnetic gap is formed between the peripheral edge surface ofthe top plate and the inner peripheral surface of each of the peripheralwall portions of the yoke.

In this case, the bottom wall portion of the yoke may have athrough-hole formed at a position corresponding to the magnetic gap tocommunicate between the outside of the magnetic circuit unit and theinside of the yoke.

Embodiments of the electroacoustic transducer according to the presentinvention will be explained below with reference to the accompanyingdrawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a sectional view of an electroacoustic transducer according toa first embodiment of the present invention.

FIG. 2 is a sectional view of an electroacoustic transducer according toa second embodiment of the present invention.

FIG. 3 a is a plan view of an annular portion of a diaphragm shown inFIG. 2.

FIG. 3 b is a sectional front view taken along the line 3 b-3 b in FIG.3 a, showing the annular portion of the diaphragm.

FIG. 4 is a sectional view of an electroacoustic transducer according toa third embodiment of the present invention.

FIG. 5 is a rear view of the electroacoustic transducer shown in FIG. 4.

FIG. 6 is a sectional view of an electroacoustic transducer according toa fourth embodiment of the present invention.

FIG. 7 is a sectional view of an electroacoustic transducer according toa fifth embodiment of the present invention.

FIGS. 8 a, b and c are a plan view, a sectional front view, and asectional side view of another magnetic circuit structure.

FIGS. 9 a, b and c are a plan view, a sectional front view, and asectional side view of still another magnetic circuit structure.

FIG. 10 is a sectional view of an electroacoustic transducer accordingto a prior art.

DETAILED DESCRIPTION OF THE INVENTION First Embodiment

FIG. 1 is a sectional view of an electroacoustic transducer according toa first embodiment of the present invention. In FIG. 1, theelectroacoustic transducer has a magnetic circuit unit including acup-shaped yoke 1 and a combination of a disk-shaped magnet 2 and a flatplate-shaped top plate 3 that are successively stacked on the innerbottom surface of the yoke 1, in the same way as in the above-describedprior art. The electroacoustic transducer further has a voice coil 4inserted into a magnetic gap formed between the inner peripheral surfaceof the yoke 1 and the outer peripheral surface of the top plate 3. Theyoke 1 is insert-molded in a resinous frame 5. A diaphragm 6 is made ofa resin sheet, e.g. PEN (polyethylene naphthalate) or PET (polyethyleneterephthalate), and has a dome-shaped central portion 6 a and an annularportion 6 b disposed underneath the central portion 6 a. The outerperipheral edge of the central portion 6 a and the outer peripheral edgeof the annular portion 6 b are joined together and form a joint portion6 c. The voice coil 4 is disposed under the diaphragm 6 and secured tothe joint portion 6 c. The inner peripheral edge 6 d of the annularportion 6 b is joined to the magnetic circuit unit. In the illustratedexample, the inner peripheral edge 6 d of the annular portion 6 b isjoined to an upper surface of the top plate 3, which constitutes themagnetic circuit unit, directly or indirectly through another component.A protector 7 is bonded to the upper end edge of the frame 5.

The inner peripheral edge 6 d of the annular portion 6 b is flexible anddifficult to handle. Therefore, a metal ring or the like may be attachedto the inner peripheral edge 6 d of the annular portion 6 b to make iteasy to perform the assembling operation.

When used as a speaker, the electroacoustic transducer, in which theannular portion 6 b of the diaphragm 6 is accommodated underneath thecentral portion 6 a thereof, is housed in an enclosure, which is acasing of an electronic device. In this case, one of spaces A and B iscommunicated with the external space, and the other space A or B iscommunicated with the space in the enclosure. The spaces A and B are cutoff from communication with each other. If not, sounds will cancel eachother out, so that satisfactory performance cannot be obtained.Therefore, both the central and annular portions 6 a and 6 b of thediaphragm 6 are required to be impermeable to air.

In the electroacoustic transducer of this embodiment, the annularportion 6 b of the diaphragm 6 is disposed underneath the centralportion 6 a thereof. Therefore, the central portion 6 a can be enlarged,and hence the voice coil 4 can be enlarged. Consequently, the soundpressure can be increased. Further, positioning of the voice coil 4 isfacilitated. In addition, because heat dissipation is facilitated, itbecomes less likely that the voice coil 4 may become loose due to heat.

Second Embodiment

FIG. 2 shows an electroacoustic transducer according to a secondembodiment of the present invention. FIGS. 3 a and 3 b are a plan viewand a sectional view, respectively, showing the annular portion 6 b ofthe diaphragm 6 of the electroacoustic transducer according to thesecond embodiment. The second embodiment differs from the firstembodiment in that the annular portion 6 b of the diaphragm 6 isprovided with air holes 6 e so as to be permeable to air. As amodification of this embodiment, the annular portion 6 b may be made ofan air-permeable material such as a mesh material. In this embodiment,the magnetic gap is filled with a liquid 8 (e.g. a magnetic fluid, orsilicone oil), thereby blocking communication between the spaces A andB.

Third Embodiment

FIGS. 4 and 5 show an electroacoustic transducer according to a thirdembodiment of the present invention. This embodiment is substantiallythe same as the second embodiment. The third embodiment differs from thesecond embodiment in that air holes (through-holes) 1 a are provided inthe bottom of the yoke 1 at positions in an annular area correspondingto the magnetic gap. When the voice coil 4 is driven to vibrate with alarge amplitude, the pressure in the space C varies to suppress themovement of the voice coil 4 undesirably. Therefore, it is preferable toprovide air holes 1 a in the bottom of the yoke 1 in the case of aspeaker in which the voice coil 4 may vibrate with a large amplitude,although such air holes 1 a are not necessary when there is nopossibility of the voice coil 4 vibrating with a large amplitude.

Fourth Embodiment

FIG. 6 shows an electroacoustic transducer according to a fourthembodiment of the present invention. This embodiment is substantiallythe same as the first embodiment. The fourth embodiment differs from thefirst embodiment in that a coil support 6 f that supports the voice coil4 is provided on the joint portion that joins together the respectiveouter peripheral edges of the central and the annular portions 6 a and 6b of the diaphragm 6. The coil support 6 f is formed in an L-shape asillustrated in the figure or in a U-shape in accordance with the heightof the voice coil 4. Although in FIG. 6 the coil support 6 f is providedon the annular portion 6 b adjacent to the joint portion, it may beprovided on the central portion 6 a adjacent to the joint portion. It isalso possible to wind a coil directly on the coil support 6 f. Thisincreases productivity. Further, it is possible to prevent the voicecoil 4 from becoming loose due to heat by bonding the voice coil 4 tothe coil support 6 f formed in an L-shape.

Fifth Embodiment

FIG. 7 shows an electroacoustic transducer according to a fifthembodiment of the present invention. This embodiment is substantiallythe same as the first embodiment. The fifth embodiment differs from thefirst embodiment in that the joint portion of the respective outerperipheral edges of the central and annular portions 6 a and 6 b of thediaphragm 6 has an annular extension 6 g formed by extending either orboth of the central portion 6 a and annular portion 6 b (both of them inFIG. 7) into a space D surrounded by an inner peripheral surface of theframe 5 and located outward of the side wall of the yoke 1. Because theouter shape of the central portion 6 a can be further enlarged close tothe outer shape of the product concerned, the effective area of thediaphragm 6 increases, and the sound pressure increases.

Although in the foregoing embodiments the present invention has beendescribed with regard to a magnetic circuit that is substantiallycircular in plan view, the present invention is not necessarily limitedto such a circular magnetic circuit. The magnetic circuit may berectangular as a whole in plan view as shown in FIG. 8. In FIG. 8, theyoke 1 has two pairs of mutually facing peripheral walls extending fromthe mutually opposing long and short sides thereof. Alternatively, themagnetic circuit may be rectangular as a whole in plan view as shown inFIG. 9. In FIG. 9, the yoke 1 has a pair of mutually facing peripheralwalls extending from the mutually opposing long sides thereof. In themagnetic circuit shown in FIG. 8, the voice coil associated therewith isformed in a rectangular shape. In the magnetic circuit of FIG. 9, thevoice coil is formed in a rectangular or oval shape.

1. An electroacoustic transducer comprising: a magnetic circuit unitthat forms a magnetic gap; a voice coil inserted into the magnetic gap;and a diaphragm to which the voice coil is connected; the diaphragmhaving: a central portion having an outer peripheral edge; an annularportion disposed underneath the central portion, the annular portionhaving an outer peripheral edge corresponding to the outer peripheraledge of the central portion and an inner peripheral edge secured to themagnetic circuit unit; and a joint portion formed at the outerperipheral edge of the central portion and the outer peripheral edge ofthe annular portion and the respective outer peripheral edges of thecentral portion and the annular portion being joined together; the voicecoil being disposed under the central portion of the diaphragm andjoined to the joint portion.
 2. The electroacoustic transducer of claim1, wherein the central portion of the diaphragm has an upwardly convexdome shape.
 3. The electroacoustic transducer of claim 2, wherein theannular portion of the diaphragm has an upwardly convex arcuatesectional configuration.
 4. The electroacoustic transducer of claim 1,wherein the joint portion of the diaphragm has a tubular coil supportextending coaxially with the voice coil, the voice coil being mounted onone of inner and outer peripheral surfaces of the coil support.
 5. Theelectroacoustic transducer of claim 2, wherein the joint portion of thediaphragm has a tubular coil support extending coaxially with the voicecoil, the voice coil being mounted on one of inner and outer peripheralsurfaces of the coil support.
 6. The electroacoustic transducer of claim3, wherein the joint portion of the diaphragm has a tubular coil supportextending coaxially with the voice coil, the voice coil being mounted onone of inner and outer peripheral surfaces of the coil support.
 7. Theelectroacoustic transducer of claim 4, wherein the coil support has anL-shaped sectional configuration having an annular support portionextending radially outward from a lower end edge of the coil support,the voice coil being in contact with both the outer peripheral surfaceand the annular support portion of the coil support
 8. Theelectroacoustic transducer of claim 5, wherein the coil support has anL-shaped sectional configuration having an annular support portionextending radially outward from a lower end edge of the coil support,the voice coil being in contact with both the outer peripheral surfaceand the annular support portion of the coil support.
 9. Theelectroacoustic transducer of claim 6, wherein the coil support has anL-shaped sectional configuration having an annular support portionextending radially outward from a lower end edge of the coil support,the voice coil being in contact with both the outer peripheral surfaceand the annular support portion of the coil support.
 10. Theelectroacoustic transducer of claim 4, wherein the voice coil is formedby being wound on the outer peripheral surface of the coil support. 11.The electroacoustic transducer of claim 5, wherein the voice coil isformed by being wound on the outer peripheral surface of the coilsupport.
 12. The electroacoustic transducer of claim 6, wherein thevoice coil is formed by being wound on the outer peripheral surface ofthe coil support.
 13. The electroacoustic transducer of claim 1, whereinthe joint portion of the diaphragm has an annular extension extendingradially outward from the joint portion of the diaphragm.
 14. Theelectroacoustic transducer of claim 2, wherein the joint portion of thediaphragm has an annular extension extending radially outward from thejoint portion of the diaphragm.
 15. The electroacoustic transducer ofclaim 3, wherein the joint portion of the diaphragm has an annularextension extending radially outward from the joint portion of thediaphragm.
 16. The electroacoustic transducer of claim 1, wherein theannular portion of the diaphragm is impermeable to air.
 17. Theelectroacoustic transducer of claim 1, wherein the annular portion ofthe diaphragm is permeable to air, and the magnetic gap is filled with aliquid.
 18. The electroacoustic transducer of claim 17, wherein themagnetic circuit unit includes: a yoke having a bottom wall portion andan annular peripheral wall portion extending upward from a peripheraledge of the bottom wall portion; and a combination of a magnet and a topplate that are successively stacked on the bottom wall portion of theyoke; the magnetic gap being formed between a peripheral edge surface ofthe top plate and an inner peripheral surface of the peripheral wallportion of the yoke; the bottom wall portion of the yoke having athrough-hole formed at a position corresponding to the magnetic gap tocommunicate between an outside of the magnetic circuit unit and aninside of the yoke.
 19. The electroacoustic transducer of claim 16,wherein the magnetic circuit unit includes: a yoke having a bottom wallportion and a pair of peripheral wall portions extending upward from apair of mutually opposing portions of a peripheral edge of the bottomwall portion; and a combination of a magnet and a top plate that aresuccessively stacked on the bottom wall portion of the yoke; themagnetic gap being formed between a peripheral edge surface of the topplate and an inner peripheral surface of each of the peripheral wallportions of the yoke.
 20. The electroacoustic transducer of claim 17,wherein the magnetic circuit unit includes: a yoke having a bottom wallportion and a pair of peripheral wall portions extending upward from apair of mutually opposing portions of a peripheral edge of the bottomwall portion; and a combination of a magnet and a top plate that aresuccessively stacked on the bottom wall portion of the yoke; themagnetic gap being formed between a peripheral edge surface of the topplate and an inner peripheral surface of each of the peripheral wallportions of the yoke; the bottom wall portion of the yoke having athrough-hole formed at a position corresponding to the magnetic gap tocommunicate between an outside of the magnetic circuit unit and aninside of the yoke.